This invention relates generally to a method for contacting a semiconductor device and to a method for the manufacture of a semiconductor device, and more specifically to a method for fabricating semiconductor devices having small contact openings etched through a planarized dielectric to underlying device regions.
As semiconductor devices become more complex, the size of individual device features is reduced. The reduction in feature size causes a number of problems which must be overcome in order to economically produce device with high reliability. One problem which is encountered, for example, is the problem of making reliable electrical contact to device regions so that the device regions may be properly interconnected to implement the desired circuit function.
An integrated circuit generally includes a semiconductor substrate in which a number of device regions are formed by diffusion, ion implantation, or the like. The semiconductor substrate, including the device regions, is overlaid with a thick insulating layer. Openings through this insulating layer allow electrical contact to be made selectively to the underlying device regions. The reduction in feature size requires the contact openings through the insulating layer to be spaced close together, to be of small diameter, and to have steep, nearly vertical, sidewalls. It is difficult, with physically deposited aluminum metallization which is generally used to interconnect the device regions, to fill reliably and reproducibly the small, steep walled openings. The high aspect ratio of insulator thickness to opening diameter makes it difficult to adequately contact the device region exposed at the bottom of the opening. It is also difficult to extend the metal into the opening without having breaks in the metal as it passes over the edge of the opening and traverses into the opening. In addition, the small device structures also are characterized by shallow junctions, and alloying of the aluminum metallization with the underlying silicon substrate often causes spikes which cause shorting of the electrical junction.
Other metals have been used in an attempt to overcome the problems which are attendant with the use of aluminum metallization. The most promising of these alternate techniques appears to be the use of selective tungsten to fill the contact openings and then the subsequent use of aluminum metallization for interconnection. The selective tungsten thus forms a "plug" which fills the contact opening so that the aluminum interconnect metallization is positioned on the top of the relatively planar insulating layer where it can be easily patterned to form the necessarily fine pitched interconnect pattern. The aluminum contacts the top of the plugs and does not have to traverse the step down into the contact openings. The aluminum is also separated from the silicon substrate by the plugs, thus avoiding the problem of junction spiking. The problem with the use of selective tungsten is that the tungsten must be deposited by chemical vapor deposition using tungsten hexafluoride (WF.sub.6) as a reactant. Even when the tungsten is deposited by the hydrogen reduction of WF.sub.6, however, the initial reaction which takes place is between the WF.sub.6 and the silicon substrate. During this reaction with the silicon, a considerable amount of silicon is consumed, resulting in tunnels in the silicon near the junction which impair the reliability of the device.
A need existed, therefore, for an improved process by which contact metallization can be applied to a semiconductor device to achieve reliable and economical contacts without the problems associated with prior art solutions.
It is therefore an object of this invention to provide an improved metallization for a semiconductor device.
It is another object of this invention to provide an improved process for the fabrication of a semiconductor device.
It is yet another object of this invention to provide an improved process for selectively depositing a conductive plug material for use in metallizing a semiconductor device.